Reproductive status in female perch (Perca fluviatilis) outside a sewage treatment plant processing leachate from a refuse dump

Reproductive failure and endocrine disruption in female perch (Perca fluviatilis) and female brook trout (Salvelinus fontinalis), naturally exposed to toxic leachate from a municipal refuse dump, has raised concerns about the reproductive status in female fish outside the sewage treatment plant (STP), which now treats the same leachate. Female perch from the receiving water, Lake Siljan, were therefore sampled in a gradient from the STP in Fornby and O¨ sterviken and compared with reference females from Isunda or Sollerfn. A high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) technique enabled the analysis of circulating steroids in blood plasma: the sex steroids progesterone (P), 17ahydroxyprogesterone (17a-OHP), androstenedione (A), testosterone (T), estrone (E1), and 17h-oestradiol (E2), the maturation-inducing hormone (MIH) 17a,20h-dihydroxy-4-pregnen-3-one (17a,20h-P), and the glucocorticoids 11-deoxycortisol (11-DC) and cortisol (C). Body and organ measurements, ratio of sexually mature (SM) females, and frequencies of body lesions, were also recorded. The percentages of SM females found in Fornby on Oct 23 (83.8%) and in O¨ sterviken on May 14 (54.0%) were lower compared with Isunda (100%). The lack of differences in gonadosomatic index (GSI) and liver-somatic index (LSI) indicated a normal vitellogenesis in SM females from Fornby and O¨ sterviken. No differences in circulating levels of steroids were observed between the sites, except at the time of spawning, when elevated P and 17a-OHP levels in females from O¨ sterviken indicated a steroidogenic shift from the synthesis of sex steroids towards the production of the MIH 17a,20h-P. The significant peak-levels of both 17a,20h-P and 11-DC in female perch from O¨ sterviken at the same time suggest that both are involved in controlling final oocyte maturation in perch. The elevated levels of androgens (A and T) in females caught on the same occasion in Fornby implied that these females were at an earlier stage of oocyte maturation, prior to the steroidogenic shift towards MIH-production. This study confirms the results of an earlier study revealing low numbers of SM female perch outside the STP in Fornby. The lack of associated effects on organ indexes and circulating levels of steroids does not indicate exposure to endocrine disrupting substances (EDSs) from the treated sewage. The consistently high numbers of SM females in the northern part of Siljan suggest, however, that natural factors are not responsible for the reproductive failures in the southern part of the lake.